Why don't Scuba Divers get crushed by all of that water above them?

Question

If that same volume of water was ice, they'd surely be dead as they wouldn't be able to cope with the weight, but why is this not the case when totally submerged in water.

Answer 1

The pressure is all around them, not only above them, as in your block of ice example. They are actually as pressurized as the water they are in - which leads to some of SCUBA's safety issues:

- nitrogen, liquid at high pressures, crosses into the bloodstream, and expands to a gas as pressure decreases (depth decreases). This is what causes the "bends," a painful and potentially deadly condition caused by nitrogen bubbles in the bloodstream.

- nitrogen actually has narcotic characteristics when its partial pressure exceeds one atmosphere. This is the cause of "rapture of the deep."

- oxygen has toxic characteristics when its partial pressure exceeds one atmosphere, and will kill you dead. This is referred to as oxygen toxicity.

For these reasons, divers at extreme depths breathe a special mixture made up mostly of inert gas (typically helium, but others are used). If you've ever noticed the squeaky voices of divers in ultra-deep submarines, that's the reason (have you ever breathed from a balloon and then tried to talk?).

Answer 2

It all depends on what the depth is. The further down they go, then the pressure starts to build and get "heavier". There is a certain depth that will start to cause nitrogen to form bubbles in the blood, which can cause very serious problems. And other things like the pressure compressing the lungs in the chest can cause less oxygen to be breathed in. This usually occurs at pretty far depth, and the divers know how to deal with the situation before they go down that far. And about comparing the water to ice, water is more dense than ice. So if the volume was the same, the ice would actually be lighter.

Answer 3

Scuba divers are unable to dive to great depths because of this crushing effect you mentioned. To go that low you need hard suits (a submarine that a man wears). Divers can go deeper under water than they can under a solid because the water pressure is pressing on all sides. So it helps to support them. The body is taking all this pressure and handling it; our structure is pretty tough, not just the bones, but also the skin. A knife can puncture your skin because it puts great pressure on a very fine point. If you spread the pressure across a larger surface area then the human body can with stand a greater pressure. If the diver were buried under a solid with equal pressure then they would only have a balancing pressure from the bottom, which would tend to crush them into a pancake. But, again our bodies are pretty strong and people have survived having concrete columns falling on them. They aren't able to take the full weight, but they can take enough weight to crush bone and still survive. It is not so much a matter of weight but a matter of weight over a square area. The larger the area, the more weight it can take.

90% of the human body is water, and water is an uncompressible liquid. If you have a gallon of water then you can put an unlimited amount of weight on it without changing that volume. The container will always fail, before the water will be compressed, even if you use a huge container carved out of one diamond. If you have 100’ of a solid on top of a diver, then the solid starts to compress so more weight is put on the body. As the solid compresses then more of it is needed to reach the 100’ level. If a diver is under 100’ of water then the only pressure is from that 100’, there will not be any extra weight since the water can’t be compressed. So 100’ of water weight is lighter than 100’ of a similar solid. 100’ of water would be lighter than 100’ of most solids because the water can’t compress and the solids can. (Ice expands because water is incompressible. If you put a can of coke in your freezer then the coke can will burst as the ice expands. Steam powered devices work well because even though the steam is a gas there is a limit to how much it can be compressed so it can provide pressure to operate the machine.)

If you put water pressure on a human body then the water pressure in the body pushes back and can stabilize. Since the water of the body isn’t compressible either it pushes back with the same force. So you only have to contend with that water weight, and you will have all the water around you helping you. It is like building a brick wall that’s only 10’ high. Your body just becomes another brick in the wall. If the brick wall increases in height then the analogy falls apart, because the brick can. The water can’t compress so it will continue to support all that weight. If you dive deep though that water pressure will mount up pretty quickly, you still have that stack of water on top of you.

200’ is a great depth to dive for scuba divers. At that depth they need to breath a special oxygen mix, to prevent the bends. Most of our atmosphere contains nitrogen (oxygen is the second most common component). Under great pressure the nitrogen is forced out of solution and forms bubbles in the blood stream. This is quite painful and if the bubbles reach the brain or heart they can cause a stroke or heart failure. So diving to this depth requires a helium oxygen mix (the helium won’t form dangerous bubbles). When the diver comes up they have to go to a more shallow depth and wait a while, or be rushed into a compression chamber where the pressure can be slowly dropped.

Because water is incompressible 100’ of water doesn’t equal the weight of 100’ of a solid (unless that solid is mostly air, like aerogel), and because your body is mostly water it can support a lot of pressure. Since scuba divers don’t go to the huge crushing depths they can survive a deep dive without getting crushed.

Answer 4

If you placed your lips around a strong vacuum pump, your body would be crushed by the atmosphere. Scuba divers must have an air supply from a compressed air tank that more than equals the hydraulic pressure of their depth. Deep sea divers must have a supply hose connected to their helmet and suit that more than equals the water pressure at their greater depth. A former deep sea diver once told me that one of his greatest fears was improper adjustment of his air supply valves. If he overinflated his suit his arms would poke straight out, preventing further adjustment and he would skyrocket to the surface and likely contract the bends which can be fatal. Only the air spaces in the body can be compressed by water pressure. The rest of the body weighs about as much as an equal volume of water and is in fact mostly water which is virtually incompressible. The weight of the water above a diver would crush him if he carried it on his shoulders but at depth water pressure is exerted equally in all directions (including up) and helps support the load.

Answer 5

Because the human body is mostly water, which is not compressible. The hollow part is the lungs, which are pressurized by the diver's air tank, so the pressure inside matches, at all times and places, the pressure from the water outside.

Answer 6

While they are in water they are pretty much weightless. The water goes around them but the deeper they go the more pressure they experience and if they go deep enough in plain scuba gear it could crush them.

There is a movie called The Abyss you may like.

Answer 7

1st off .... ice doesn't weigh more than water ... it's the same weight with more volume....

2nd ... they don't get crushed in the same way air pressure (14.7 lbs/sq ") doesn't crush us.... the pressure is all around us.... the water pressure affects air in our system, but our bone structure is strong enough to sustain at least 2 atmospheres of pressure underwater....the air in our system has a harder time

Answer 8

They don't go deeper that 100 feet. If a diver went 1000 feet deep without being in a submarine, they would be crushed.

Answer 9

Because the human body is something like 80% water anyway.

Answer 10

If they went deep enough, they would be crushed... when I get down to 100 feet or so I start feeling pain in my ears even though I'm trying to stabilize my pressure..